1. Technical Field
The present invention relates to image-transfer technologies.
2. Related Art
When transferring images having a high resolution between image-processing apparatuses such as printers, personal computers and digital still cameras, the processing load for image transfer is high due to there being a large amount of data to process. Therefore, the amount of data to be transferred is reduced by compressing the image or reducing the resolution of the image, prior to transferring the image. Here, in a case in which, prior to being transferred, the resolution of an image including a text portion and a portion other than the text portion (hereafter, a graphic portion) was evenly reduced, a deterioration in image quality can occur, such as unevenness in the width of lines or tapering in the text portion of the image after the expansion of the image. In response to this, a method has been proposed in which a text portion and a graphic portion of an image are separated, respectively reduced to appropriate resolutions, and then transferred. Then, on the reception side, after increasing the resolutions of the respective portions so that they are made to match, the portions are combined to re-form the image (see, for example, JP-A-2002-176552).
FIG. 13 is an explanatory diagram that schematically illustrates an image-transferring method of the related art. In FIG. 13, an area A within an image F1 is shown in an enlarged manner. On the sending side, the area A is separated into a text portion Pa and a graphic portion Pb, the text portion Pa and the graphic portion Pb are respectively turned into a image f1 having a high-resolution and an image f2 having a low-resolution, and the images f1 and f2 are then transmitted. On the receiving side, after converting the received image f2 to the same resolution as the image f1, a composite image F10 having a high resolution is obtained by combining the image f1 and the image f2. At this time, there has been a problem in that loss of data occurs in areas B corresponding to the boundary between the text portion Pa and the graphic portion Pb in the composite image F10.
A method has also been considered in which, when an image is to be transferred, the amount of data is reduced by reducing the number of bits used to represent the tone of each pixel of the image, without causing the resolution of the image to be reduced. However, in this case, on the receiving side, the hues of the original image (particularly those of a graphic portion) cannot be faithfully reproduced and the quality of the image is severely deteriorated.
The above-described problems can arise not only in image transfer between different image-processing apparatuses but also in image transfer within a single image-processing apparatus (for example, in image transfer from a unit functioning as a scanner to a unit functioning as a printer within a multifunction apparatus).